Field of Invention
The invention relates to the field of photography, and more specifically to mechanisms and methods for reducing picture blur by curtailing movement of film relative to the camera during an exposure sequence. The invention also relates to a method of assembling a camera including features for reducing picture blur.
Description of the Prior Art
The invention is applicable to many camera designs, but has particular utility in low cost and single use cameras according to the preferred embodiment of the invention.
Single use cameras are assembled from relatively inexpensive components and sold with the film included. During manufacture, a film cartridge, typically in a standard 35 mm size and format, is positioned in a camera take-up chamber. Most of the film is then pulled from the cartridge, positioned across an exposure plane and prewound into a film supply chamber opposite the exposure plane from the take-up chamber. In use, camera mechanisms advance the film sequentially, one frame for each picture, from the supply chamber across the exposure plane and back into the cartridge. The advancing mechanism typically is a thumb wheel that engages a spool inside the cartridge and rotates the spool to draw the film, attached to the spool, from the supply chamber into the cartridge.
Although simple in construction, single use cameras include suitable mechanisms for metering the film to position the individual frames properly in the exposure position. Perforations along an edge of the film engage and drive a sprocket wheel when the film is advanced. The sprocket wheel includes a notched cam that rotates with the sprocket, one revolution for each film frame. When a film frame is properly positioned for exposure, an arm on a film metering lever pivots into the notch. This same pivotal motion moves another arm on the same lever into engagement with teeth around the periphery of the thumb wheel and thereby prevents further advancement of the film. The film also is prevented from backing up toward the supply chamber. An anti-backup arm is biased to ratchet against the thumbwheel teeth, preventing rotation of the wheel in the reverse direction. The film is thus locked against forward movement by the metering lever and against backward movement by the anti-backup arm.
An exposure is initiated by depression of a trigger button that releases a latch constraining a high energy striker. The striker drives a shutter blade to open an exposure aperture and expose the film. The striker also pivots the metering lever from the cam notch, and releases the thumb wheel and film for advancement. When the sprocket is rotated again by engagement with the film perforations, the cam resets the high energy striker, latching it for the next exposure.
A single use camera of the type described above is disclosed, for example, in U.S. Pat. No. 5,235,366, issued Aug. 10, 1993.